Isostatic presses are used in different kinds of industry. One example is the food industry, wherein foodstuff is typically subjected to a pressure of 1000-10000 bar, such as 6000 bar, in order to inactivate micro-organisms and thereby prolong the shelf life of the foodstuff. In view of the high pressure levels used in these presses, they are commonly referred to as high-pressure presses, some of which are operable at pressures as high as 15000 bar. Isostatic presses may also be used in producing articles such as turbine blades for aircraft or artificial hip joints for implantation into persons.
An isostatic press comprises a force-absorbing pressure vessel enclosing a pressure chamber. The substances or articles to be treated are placed into the pressure chamber which is subsequently closed. A pressure medium, such as a liquid or a gas, is supplied into the pressure chamber for creating the desired pressure in the pressure chamber. The articles or substances will be affected by the pressure medium isostatically, i.e. equally from all directions. Some presses are further provided with a protective liner on the inside of the cylindrical force-absorbing pressure vessel wall, for instance in order to minimize or prevent corrosion of the pressure vessel wall.
An example of a press provided with a liner is disclosed in international patent application WO 95/21690. More specifically, the press comprises a first outer thick cylinder element of a high-tensile steel inside of which is arranged a package constituted by a thin inner safety liner and a surrounding supporting liner. A channel between the safety liner and the supporting liner provides a means of fracture indication if a fracture has occurred on the thin safety liner.
Even though the press of WO 95/21690 has many advantages, it presents a relatively complex press. The inside of the thick outer cylinder element is slightly conical in order to provide a required compressive prestress to the safety liner when it is inserted into the thick cylinder element. However, since the safety liner is a replaceable protective liner which is thin, it cannot be driven alone into the thick outer cylinder element. Therefore, the safety liner must first be inserted into the supporting liner, this liner assembly not yet being prestressed. Then the liner assembly is forced into the conical space of the thick outer cylinder element, whereby the liner assembly becomes radially prestressed. Furthermore, WO 95/21690 is limited to fracture detection of a thin liner.